This invention relates to magnetic slot wedges inserted in slots of a stator core of a dynamo-electric machine for preventing coils embedded in the respective slots from getting out of them, and more particularly to such magnetic wedges comprising an insulating material and a magnetic material combined with the insulating material.
Magnetic wedges are usually inserted in respective slots of a stator core for the purpose of improving the efficiency and power factor of electric motors and reducing noise due to electromagnetic vibration. The insertion of the wedge in each slot corrects the magnetic unbalance between each slot opening of the stator core and core teeth and accordingly, reduces the magnetic flux distortion of an air gap between the rotor and stator, resulting in improvements of motor characteristics.
Since a slot wedge at an initial stage of the prior art comprises a material formed from iron powder by way of the compression molding, it has a relatively large thickness. The motor characteristics can usually be improved in proportion to an amount of coil embedded in each slot of the stator core. However, the prior art wedge having the relatively large thickness reduces an effective cross sectional area of each slot, offsetting the effect of inserting the wedge. Further, the strength of the wedge is low such that the wedge is likely to be broken by an external shock in the step that it is inserted into the slot or in the state that it has been inserted in the slot. To overcome these disadvantages, Japanese Laid-open (kokai) Utility Model Registration Application No. 59-18548 discloses a thin magnetic wedge. This thin magnetic wedge comprises a thin insulative sheet member and a magnetic powder such as ferrite coated on the thin insulative sheet member to be integrated with it. However, a large automated expensive equipment is required for coating the magnetic powder on the thin insulative sheet member. Further, when the magnetic powder is coated on the insulative sheet member too thick, the magnetic layer is removed from the insulative sheet member in a step of inserting the wedges in the slots. Additionally, since the face of the insulative sheet member on which the magnetic powder is coated faces the coil side within the slot, the voltage withstanding property of the coil is reduced and further, the coils are damaged by the magnetic layer.
Japanese Laid-open (kokai) Patent Application Nos. 58-19138, 58-22554 and 59-175350 each disclose magnetic wedges employing amorphous alloys. In these magnetic wedges, amorphous sheets are laminated so that the lamination has a trapezoidal longitudinal cross section. Each sheet is bonded to an adjacent sheet by a bonding agent or a synthetic resin layer containing a magnetic powder is interposed between each sheet and its adjacent one so that an integral construction is obtained. Furthermore, a magnetic wedge is disclosed which is made by molding an amorphous magnetic fiber with an organic bonding agent into a predetermined integral shape. However, to make these laminated magnetic wedges, many kinds of amorphous sheets having different width are required and each of many amorphous sheets needs to be bonded to its adjacent sheet. Consequently, many manufacturing steps are required and a sufficient strength of the magnetic wedge cannot be secured by the bond strength. Further, since the magnetic wedge is integrally formed by bonding each sheet to its adjacent one, by interposing the synthetic resin layer between each sheet and its adjacent one or by molding the amorphous magnetic fiber with the organic bonding agent, the volume of the magnetic wedge is increased, resulting in worsening the motor characteristics and increasing the motor size.